400 Mr. J. 8. Bowerbank on the Spongiade, 
self that in the polypes mentioned above, the mner surfaces of the 
polype-cells, of the appendices of those processes described in the 
Cellularia reptans and scruposa, of the bird-head processes, of 
the spines, and of the canals running along the lateral surfaces 
of the polypidom in Flustra avicularis, ave all lmed by a fine 
membrane. This membrane in old specimens, and when the 
polypes are dead, often presents numerous and pretty large cells, 
generally of a pale colour, at other times having a slightly yel- 
lowish or brownish tinge, adhering to its free surfaces. In one 
specimen these cells had accumulated in such quantities within 
some of the spines in Flustra avicularis, as to produce consider- 
able bulgings and excrescences. The growth and nutrition of the 
hard parts of the polypidom must be chiefly due to this mem- 
brane. 
EXPLANATION OF PLATE XII. 
Fig. 1. Magnified view of the posterior portion of the upper end of a branch 
of the polypidom in Cellularia reptans. It is slightly elevated on 
the left side, so that the polype-cells of that side are better seen 
than on the other. 
Fig. 2. Three appendices to the cells in Cellularia reptans. 
Fig. 3. Magnified view of four polype-cells of Cellularia replans seen on the 
anterior surface. 
Fig. 4. Magnified view of polype in Cellularia reptans when folded up in 
its cell. 
Fig. 5. Magnified view of this polype when expanded. 
Fig. 6. Magnified view of the anterior surface of the upper part of one of 
the branches of the polypidom in Cedlularia seruposa. ‘The polype- 
cells are in this drawing also more distinctly seen on one side than 
on the other. 
Fig. 7. Magnified view of three appendices to the polype-cell in Cellularia 
scruposa; b, b, bis, views of the process bearing the hair-like pro- 
longation in two different positions. 
Fig. 8. Greatly magnified view of head and upper part of stalk in Pedicel- 
lina echinata. 
Fig. 9. Greatly magnified view of the ciliated ova of Pedicellina echinata, 
Fig. 10. Magnified view of polype in Crista chelata. 
Fig. 11. Magnified view of polype-cells in Aleyonidium parasiticum. 
Fig. 12. Magnified view of bird-head process in Flustra avicularis. 
Fig. 13. Magnified view of ova in Flustra avicularis. 
XLIV.— Observations on the Spongiadee, with descriptions of some 
new genera, By J. 8. Bowrrzann, F.R.S., L.S8. &e. 
[ With two Plates. ] 
Tue microscopical examination of several hundred species of the 
Spongiade has led me*to believe it possible that a series of cha- 
racters may be obtamed from the anatomical structure of the 
skeleton, which, from their constancy and striking peculiarities, 
will enable us to establish genera, based upon more certain cha- 
